1. Field of the Invention
This invention relates to a headbox in a paper making machine. More particularly, it relates to flow restraining elements in the headbox.
2. Description of the Prior Art
A conventional headbox for a paper making machine which is described in one of the applicants' copending U.S. application Ser. No. 662,817, filed Oct. 22, 1984, which is a continuation of application Ser. No. 484,694, filed Apr. 19, 1984, now abandoned, is shown by way of example in FIG. 1. It comprises a top plate 2 and a bottom plate 3 defining therebetween a chamber in which a plurality of flow restraining elements 1 are provided one above another. Each element 1 is held at one end by one of a plurality of grooves formed in a perforated plate 4 disposed upstream of the elements 1. The flow of a raw paper liquid in the chamber maintains the elements 1 in their positions shown in FIG. 1. The elements 1 define a plurality of paths 5. Those portions of the paper material which flow through the paths 5 meet downstream of the elements 1, and ran paper liquid is ejected onto a wire not shown after its degree of opening has been controlled by a slice lip 6.
A plurality of paths defined by a plurality of flow restraining elements enable the effective dispersion of fibers in the liquid with a small head loss and thereby the production of paper of high quality.
The known flow restraining elements as shown at 1 in FIG. 1, however, have a number of drawbacks. They are difficult to make because of their large variation in thickness defining narrow neck portions at the positions of narrowest thickness. They easily get warped along their width. Correctly sized paths are, therefore, difficult to define. The elements break easily at any portion of reduced thickness (neck portion). Those portions of the elements at which they are connected to the perforated plate are so small in thickness that they easily get deformed and are difficult to attach to, or detach from, the perforated plate.